In order to achieve your goal, I would suggest you to try the below options:
- Simulate a Button click, or other control of the second panel event, when certain action is performed in the first panel.
- Manually update the second RadAjaxPanel UpdatePanel. This approach is rather the same as using ASP:UpdatePanels.
For your convenience I am attaching a sample project illustrating how you could implement both of the above.
Let me know if this helps.
the Telerik team